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Climate Change

Evidence continued to strengthen in 2005 that Arctic temperatures are rising more rapidly than the global average, and that the rate of increase may accelerate due to feedback mechanisms. In the northern hemisphere, the highest increases over average temperatures occurred in northwest North America and the northern Far East of Russia. In the Yukon Territory and Alaska, summer temperatures reached record highs in 2004 and were above normal in 2005. Alaska and Yukon also experienced record high areas of burned forest in 2004 and near record high areas in 2005 – a total for the two years of about 65 000 km2, which comprises 25 to 30 per cent of all forested land and an area roughly the size of Ireland or of Sri Lanka. Forest fires of similar size burned large portions of Siberia in 2002 and 2003 (Juday 2005). There were new findings this year on feedback mechanisms that could stoke global warming:

● In western Siberia, a massive peat bog of nearly one million km2 in area, has begun to melt over the past three or four years. This will release huge amounts of the greenhouse gas methane into the atmosphere, which in turn will result in further climate warming. Estimates put the amount of methane frozen in the Siberian peat bog at 70 billion tonnes – one quarter of all the methane stored in land, worldwide (Pearce 2005).
● A study in Alaska found that 95 per cent of the recent increases in summer temperatures in the region are attributable to increases in the length of the snow-free period (about 2.5 days per decade since the 1960s) (Beringer and others 2005, Chapin and others 2005). This leads to warming because the darker, snow-free land reflects less of the sun’s radiation than the light-coloured snow. The warmer summers promote increased growth and expansion of shrubs, which also have an overall warming influence. There was a record reduction in summer Arctic sea ice in 2005 (Box 1). Experts predict that if current trends continue, the Arctic Ocean will be completely ice-free by the end of this century.

In the Antarctic, by contrast, there has been only a slight decline in the extent of sea ice between 1973 and 2004. This may be due to oceanographic and sea ice dynamics which differ from those in the Arctic (Flato and Boer 2001). A recent study indicates that the Antarctic’s response to climate change is only being delayed and that a marked reduction in the extent of sea ice is likely later this century (Goosse and Renssen 2005). Future changes in the extent of Antarctic sea ice cover may adversely impact krill, the small crustaceans that form the base of the Antarctic marine food chain. The extent and duration of Antarctic sea ice influences both krill recruitment (the proportion that survives to maturity) and spawning (Siegel and Loeb 1995). Although adult krill can withstand long periods of starvation, juveniles cannot and sea ice production is vital to their survival because their primary food source is algae that live in the sea ice (Arrigo and Thomas 2004).

A decline in krill will affect other species, including seabirds. Reduction in three seabird species and in penguin nests in some sub-Antarctic Islands have already been observed, and studies show a correlation among sea ice, availability of krill, and numbers of breeding pairs of birds (Woehler and others 2001).

Polar terrestrial and ocean ecosystems will be affected dramatically by the reduction in sea ice and significant global impacts are predicted. The projected changes will impact surface energy and moisture budgets in the Polar Regions and will affect atmospheric and oceanic circulation (ACIA 2005, Johannessen and others 2004). Attention also focused in 2005 on the large stores of freshwater ice in the Antarctic and Greenland ice sheets. Changes in the mass balances of these ice sheets would have global consequences, such as changes in sea level and salinity. Meltwaters from polar ice sheets – mainly the Greenland Ice Sheet – have been making a small contribution to sea level rise of 1–2 mm per year over the past century (Alley and others 2005). Concerns have also been raised about the recent acceleration of melting and breakdown along the margins of the West Antarctic Ice Sheet (Box 2), which are disintegrating at an unprecedented rate in some areas (Shepherd 2004). Environmental changes also directly affect the lives of Arctic residents, especially indigenous peoples (ACIA 2005). According to local observations changes on the land and sea related to the warming Arctic climate are already affecting indigenous peoples – for example, travel conditions and the availability of water (Box 3).

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